Means for producing synchronization and regeneration of electric telegraph signals



Oct. 3, 1944. A. KAHN ErAL 2,359,649

MEANS FOR PRODUCING SYNCHRONIZAIION AND REGENERATION OF ELECTRIC TELEGRAPH SIGNALS Filed Nov. 19, 1942 5 Sheets-Sheet 1 Ffm/Tf@ /Ic/f END PuAsf UMCOR/Pfc 76a 600m/URK 57m/anna INVENTORS frela/v Warne/ 7502?/ BY ../wvW

ATTORNEY Oct- 3, 1944- A. KAHN ETAL 2,359,649

MEANS FOR PRODUCING SYNCHHONIZA'TION AND REGENERATION OF ELECTRIC TELEGRAPH SIGNALS Filed Nov. 19, 1942 5 Sheets-Sheet 2 ATTORN EY Oct. 3, 1944. A. KAHN ETAL 2,359,649

MEANS FOR PRODUCING SYNCHRONIZATION AND REGENERATION OF ELECTRIC TELEGRAPH SIGNALS Filed Nov. 19, 1942 5 Sheets-Sheet 5 ATTORNEY .Oct 3, 1944. A KA-HN ETAL 2,359,649

MEANS FOR PRODUGING SYNCHRONIZATION AND REGENERATION 0F ELECTRIC TELEGRAPH sIGNALs Filed NOV. 19, 1942 5 Sheets-Sheet 4 A I BY 0'00'0'0'0'0'0 0' o o MWC/t -ATTORNEY 06. 3, 1944. A. KAHN ETAL, 2,359,649

MEANS FOR PRODUGING SYNCHRONIZATION AND REGENERATION OF'ELECTRIC TELEGRAPH SIGNALS Filed Nov. 19, 1942 5 Sheets-Sheet 5 o C1A @I TQQ @I I@ o Bgvymv www@ Iv II am 213 215 216 Llc P 5 P/I I I I I I I I I I I C o 2,8/

Qw Veel j/222 225 P224 I/225 /o .0 I I I I I I o 2 2 PJ Is/ao Y2I9 V220 /0 o Rj v l I l I 0 229 5 227 228 E30 o O Aard EiNVlNbTORS fw-Irm/ ATTORNEY Patented Oct. 3, 1944 MEANS Fon PnoDUcmG sYNcnRoNI'zA- 'rioN AND REGENEmi'rIoNv oF ELECTRIC TELEGRAPH SIGNALS Alfred Kahn, Hollis, and Warren A. Anderson, New Dorp, Staten Island, N. Y., assignors to Radio Corporation of; America., a corporation of Delaware Application November 19, '1942, Serial No. 466,094

(Cl. FX8-69.5)

. 21 Claims.

This invention relates to electric telegraph systems.

In prior artlphase control systems, such as disclosed in the application of Warren A. Anderson, led April 30, 1941, Serial No. 391,077, now

Patent No. 2,309,622, granted Feb. 2, 1943,. failures to correct the phase displacement between an incoming signal having multiple marks and the local source of frequency occasionally resulted, as when the local alternating source was 180 out of the intended phase relation. This could occur, for example, when the system was first started in operation with this 180 phase displacement, though it might sometimes occur through other accidental causes.

It is an object of the present invention to provide means for establishing the desired correction under all conditions of phase displacement. Another object of the invention is to provide for phase correction at all times even though' the local source is reversed from its correct phase relation with the signal.

Another. object of the invention is to provide improved means for phasing the receiving devices with those at the transmitter.

Another' object is to provide improved means for regenerating the received signal, in combination with means for producing the proper phase .relation between the local source of frequency and the incoming signal.

Another dbject is to generate voltages at the time-center of the received signal marks and spaces for starting and ending the regeneration and to provide means for preventing voltages formed at the start of the signal marks from interfering with this regeneration.

Other objects of the invention will appear in the following description, reference being had to the drawings, in which:

Figure 1 is an illustration, chiefly in block diagram, of our invention. y

Figure 2 illustrates the circuits of the local source of frequency and the motor circuits for changing its phase.

Figure 3 is a circuit diagram illustrating the invention as used for producing synchronization and phasing of the receiving apparatus.

Figure 4 is a diagram of th circuits for regenerating the received signals.

Figure 5 contains a series of graphs illustrating.

the principles of the invention.

Figure 6 contains graphs illustrating the principles of the action of the pulse-forming condensers of the regenerating apparatus.

The invention will first be explained in a general manner in connection with Fig. 1, in which it has been applied to a single channel for a synchronous printing system, but this is for illustrative purposes only, as it is equally well capable of use in multiplex and other forms of communication.

It is usual to have at each local station of a communication system bothl transmitting and receiving apparatus. Fig. 1 illustrates, chiey in block diagram, such a station. While the present invention relates primarily yto the receiving end of the system, a brief description of the transmittingr apparatus will be given to enable one vbetter to understand the improvement at the receiving station.

A tape transmitter I, or other desired signaling apparatus, applies positive and negative voltages to the segments of the distributor 2, though of course on-and-oif signals of one polarity could equally Well be used. The distributor is l shown, but by way of example only, asy adapted to a seven-unit code system. A brush 3 is rotated by a synchronous motor 4 at the desiredspeed.vv For purposes of illustration it will be vassumed that the brush is moving at a baudrate 'of 426/1 cycles per second. This is the fourteenth sub-harmonic of the frequency` of the tuning fork standard frequency indicated at 5. The output of the frequency standard 5 is fed into a multivibrator or othery suitable frequency divider 6, which has suitable wave-shaping devices for producing an output electromotive force of approximately sinusoidal form at this sub-harmonic frequency.

The output of the frequency divider 6 is fed into drive amplifier l and `its output feedsr into the synchronous motor 4. The drive from the motor 4 is such that the brush 3 passes over one of the contacts of the'distributor 2 during one complete cycle of thealternating electromotive force from the amplifier 1. In other words, the frequency of the driving electromotive force is the same as the baud rate of the telegraph system, which is equal to twice the channel keying frequency, since it takes two bauds to make a keying cycle.

The signals from the tape transmitter are fed in succession rby the rotating brush -3 to keying devices and other apparatus for radio trans- `mission to the distant receiver, though, of course,

the signals could equally well be used in wire telegraph transmission.

vSignals sent out from a' distant station, as just been described in connection with the local transmitting apparatus of Fig.'1, would be received, detected, amplified and converted to tone The signals in the output of I3 will usually distorted due to multipath and other conditions and they are therefore regenerated at I4 to the original form sent out by the distant transmitter,

as will be later described in detail.

The output of the regenerator I4 is fed into relay I5 so that the tongue I6 contacts the positive terminal of the relay for mark and the negative terminal for space, or vice versa, as the case may be. Thus, signals equivalent to those transmitted are fed to the rotating brush I1, driven by synchronous motor I8 of a distributor system I9, similar to the distributor of the distant transmitting apparatus, which, as'stated, is similar to the local transmitting distributor 2.

'The transmitted signals are thus picked off and fed to the seven-unit printer 20, such as described, for example, in the patent to J. A. Spen cer, No. 2,274,103, February 24, 1942.

Local or function rings would, of course, be used in connection with the transmitting and receiving distributors, such as 2 and I9, but the distributors are not parts of our invention and for simplicity they have been omitted.

While the tuning fork standards at the distant transmitter and at the local receiver are designed to maintain the same frequency within one part in a hundred thousand, it is impossible to construct two frequency standards so that they will continually remain in absolute synchronism and phase. The tuning fork standard at the transmitter sets the transmitting frequency, without correction to any other standard, and the output of the tuning fork standard at the receiver is cor-l rected to have exactly this frequency with constant phase relationship thereto.

To provide for the phasing and synchronizing of the local frequency, the output of the local tuning fork standard 5 is fed into an automatic motor-operated phase shifter, generally indicated at 2|, and the correctly phased local frequency is fed into frequency divider 30, such as the wellknown multivibrator with an appropriate filter, which reduces the 600 cycle frequency to 425/1 cycles per second of sinusoidal form. The output of this frequency furnishesI the local frequency for driving the receiving distributor brush, in the printer example assumed, and also produces a plurality of short pulses for maintaining correct phase relation with the incoming signal. It is also used to supply pulses for the regeneration of the received signals.

' In the first of these uses, the frequency divider "530 is connected to amplifier 3i and the amplified j' output is fed into synchronous motor I6 of the vreceiving distributor I 9.

VvIn the second use, the output of divider 30 is fed through a phase shifter 32 to a front-end pulse-forming circuit 33 and directly to a backend pulse circuit 34. The frontand back-end pulses are obtained from the local corrected fre- `quency source 30 and separated the desired amount by the manual phase shifter 32. These back-end pulses with pulses produced from this signal controls a relay 36, which applies local voltage causing phase shifter 2l to maintain the desired phase of the 600 cycle frequency source. This likewise controls the phase of the 42/1 cycle frequency source 30. Eithery A. C. or D. C. voltage may be used to control phase shifter 2l, but by way of example the latter has been indicated.

In the third use, the local corrected output of divider 30 is connected to the signal regenerator I4 to produce pulses in the exact centers of the rectified signal bauds. These pulses are then used to control `the regeneration of the signals. The regenerated signals operate the relay I5 connected to the distributor brush I1 of distributor ,I9 and the received signal is printed at'ZIl.

Fig. 2 illustrates the circuits of the local source of frequency and phase control shown at 5 and 2| of Fig. 1. In Fig. 2 a tuning fork 31, in conjunction with oscillator stage 38and amplifier 39, feeds 600 cycle frequency into transformer 40, the secondary of which has its midtap grounded and its terminals connected to a con-' denser 4I in series with a variable resistance 42. The upper terminal of condenser 4| is connected to ground through the primary of transformer 43 and the lower terminal thereof is connected to ground through the primary of transformer 44.

The terminals of the secondary of transformer 43 are connected to one pair of opposite quadrant plates 45, 46 of the phase shifter 41 (block 2l of Fig. 1) and the terminals of the secondary of, transformer 44 are connected to the other pair of opposite quadrant plates 48, 49 of said phase shifter. The adjustment andterminal connections are such as to give, at a given instant,

relative phase angles of zero for plate 46, 90 for plate 45, 180 for plate 49, and 270 for plate 46. The rotary plate 50 is so positioned as to constitute a plate of a condenser in conjunction with one or more of the four stationary plates. 'This rotary plate is adapted to be moved by a. motor unit 5I, shown diagrammatically. The drive is such as to insure that the adjustment will be kept after the motor stops rotating under control of relay 36 of Figs. 1 and 3. The rotating plate 50 is connected to the gri of one tube of dual amplifier-limiter stage 52 and the plate 43 is connected to the grid of the other tube, The grids are also connected through appropriate resistances to ground. The cathodes are grounded through the well-known self-bias resistor. The stage 52, shown in detail, is one of a number of similar stages constithe voltage between the terminal 54 and ground local frontand back-end pulses are fed into a differential circuit device 35, later explained in detail. The rectified signal from device I3 is also fed into the differential circuit'device 35.

A combination of the locally derived frontand has the corrected frequency of 600 cycles, while' the voltage between the terminal 55 and ground has the uncorrected frequency, but this is substantially 600 cycles except for the slight drift inherent in the frequency standard. With the construction indicated, the potential between rotor plate 50 and ground will be converted into a rectangular wave and applied to frequency divider 20. This wave will have the corrected frequency and phase. The potential between stator plate 48 and ground will likewise be amplified and converted to rectangular wave form, but it will have the uncorrected frequency.

Fig. 3 is a detailed circuit diagram of blocks 32, 33, 34 and'35 of Fig. 1. The purpose of the circuits of this gure is to control the relay 36 for energizing the motor unit 5I (Fig. 2) and rotate the condenser plate 50 in one direction or the other to maintain the local source of 428/1 frequency in constant phase relation with the incoming signals. v

The corrected 426/1 cycle voltage from 30 of Fig. 2 is fed into phase shifter 32 (see also Fig.l

chain of circuits and similarA parts will be given the same reference characters with the letter a appended thereto, so the l'connect'ons will be un- Y derstood without detailed explana on.

hasI the corrected 426/7 cycle frequency. The A plateof this amplifier is connected to the plus B supply terminal through a suitable resistance 65. Pentode limiter-amplifier 66 has its control grid coupled through resistance 61I and condenser 68 to the plate of tube 62. Resistance 69 is connected between ground and the condenser end of resistance 61. 'I'he plate oi' pentode 66 is connected through resistance 10 to the plus B supply. 'I'he screen and suppressor grid connections of this pentode are well known and need not be explained. The -sine wave input of the 42e/'z cycle voltage is converted by pentode 66 into rectangular wave'form in its plate circuit.

A diiferentiating circuit. consisting of condenser 12 and resistances 13, 14, is connected to the plate of pentode 66 and to the input grid of p'entode 15. One end of resistance 14 is grounded to the plus C terminal and the other end is connected to the minus C terminal. The positive pulse produced by the differentiating circuit produces an inverted pulse in the plate voltage o1' the pentode 15 and to reverse this, an inverter triode 16 has its grid coupled to the plate of pentode through condenser 11. connected to the plus B terminal through resistance 11. The grid is connected to a point in potentiometer resistance 18 which is connected between the plus B terminal and ground.

The chain of circuits at the top of Fig. 3, as just described, produce the end pulses of the front-end portion of the bauds, called herein the E. F. E. pulse, whose function will be later described. There is a similar chain of circuits at the bottom of Fig. 3 for producing the pulses at the start of the back-end portion of the bauds, called herein the S. B. E. pulses. Since the two chains of circuits are identical, except for the connections to the phasing device 32, similar parts will be given the same reference characters but with the letter a appended thereto and the circuit of the second chain will be understood without detailed explanation.

Before explaining the circuits connected to the output of the said two chains of circuits, it will be said that the rectangular signal voltage from block I3 of Fig. 1 will be used to control the passage of the pulses to said output by applying the signals to load resistance 19 of Fig. 3, with grounded end positive. The .ungrounded end of this resistance is connected to one end of `resistance 80. The other end of this resistance is connected to the plus B terminal.

A keying tubeI 8| h/as/ its grid connected to 'an intermediate point in resistance 80 and its caththe junction of resistances 82 and 63. A keying tube is similarly connected to the said lower The plate is The circuits already described in Fig. 3 produce the primary control potentials. The associated relay circuits will now be described.

At the upper right-hand part of Fig. 3, a. pair of thyratrons 84, have their anod'es connected 'to the plus B terminal through resistances 86, 81, respectively, and their cathodes grounded. The plates of the thyratrons are connected by a commutating condenser 88. A condenser 89 "is con-- nected between ground and the plate of thyratron 65 through diode 90 and resistance 9|. The connection is such that the condenser will charge at certain times through the diode from the plus B supply, but cannot discharge therethrough. The discharge of the condenser 89 can take place only through thyratron 92 when itis made conducting.

This thyratron has no source of plate voltage except the, voltage on the condenser 89 and it will therefore cease conducting 'when the con-V denser dscharges down to the extinguishing voltage of the thyratron.

At the lower right-hand corner of Fig. 3, a second pair of mutually quenching thyratrons, a diode and a condenser, with its discharging thyratron, are similarly connected and have similar reference numerals with the letter a appended thereto to indicate such similarity. The connections will be understood without detailed explanation.

At the right center of Fig. 3, a pair of ampliiier triodes 93, 94 have their plates connected in parallel to the plus B supply and their cathodes connected in push-pull to ground through resistances 95, 96, respectively, and the coils of relay 36. Integrating condensers 91, 98 are connected between ground and the cathodes of tubes 93, 94, respectively.

The grids of tubes 93, 94 are connected to the ungrounded end of the signal load resistance 19 through resistances |0|, |02l respectively, ofthe order of 2 megohms. The input circuit disclosed is such as to block the tubes 93 and 94 on signal mark and unblock them on signal space. The grids of these tubes are also connected to the ungrounded ends of condensers 89 and 89a through resistances |03a, |04a, respectively, of

the order of 10 megohms.

The connections thus far described in Fig. 3 are functionally those disclosed in said Anderson application Serial No. 391,077, which sometimes would not effectively correct phase deviations when, in starting the system, the local source of frequency was reversed with respect to the rectied signal. 'I'his reversed the position of the E. F. E. and S. B. E. pulses and prevented the phase correction from taking place until the phase of the local source was manually reversed.

To render the phase correction immune to this occasional defect, we use an additional thyratron |03 (see lower right-hand corner of Fig. 3) having its grid connected to the junction of the resistances |04, |05 bridged between minus C and the plate of thyratron 85a. The circuit is completed to plus C through resistance |05'. Theanode of thyratron |03 is connected through condenser |06 to the anode of thyratron 92a and also the cathode of thyratron |03 is grounded and the anode is connected to the plus B terminal through resistance |01.

The upper and lower chains of pulse-forming circuits have the following connection to the thyratron tubes:

The anode of ampliiler tube 16 is connected through condenser |08, resistances |06', |09 to the minus C terminal and the grid of thyratron 55a is connected to the junction point of these resistances. The anode of tube 16 is also connected through condenser and resistancel to the grid of thyratron '92; which is also connected to receive a negative bias from the minus C supply I I2. 'I'he anode of tube 16 is further connected through condenser ||3 to the grid of thyratron 64 through resistance I |4 and to the anode of thyratron |03 through resistance ||4a. The grid of thyratron 64 is connected to the negative terminal of the negative bias supply.

In the lower chain of pulse-forming circuits, the anode of amplifier tube 15a is connected to the grid of thyratron 92 through condenser ||5 and resistance ||6. It is also connected through condenser ||1 and resistance ||6 to the grid oi' thyratron |03.

In additionv to 'the described circuits for producing the E. F. E. and S. B. E. pulses, still another circuit is provided for producing the start of mark and the end of mark pulses. 'I'hese are herein designated as the S. M. and E. M. pulses, respectively. For this purpose the upper end of signal load resistance 19 is connected through resistances I I9 and |20 to the plus B terminal and the grid oi amplier tube |2| is connected to the junction point of these resistances. The cathode of this tube is grounded and the anode is connected to the plus B terminal through resistance |22.

Amplier tube |23 has its grid connected to the plate of tube |2| through condenser |24. The grid is given an appropriate bias by connecting it to a point between the potentiometer resistances |25, |26, connected between the plus B terminal and ground. The plate of tube |23 is connected to the plus B terminal through resistance |21.

The plate of tube |2| is connected through condenser |26 and resistance I 29 to the grid of thyratron 92a, which is connected to the minus C terminal through resistance |30. This plate is also connected through condenser |3| and resistance |32 to the grid of thyratron 64a, which is connected to the minus C terminal through resistance |33. The plate of tube |23 is connected through condenser |34 and resistance |35 to the grid of thyratron 65, which is connected to the minus C terminal through resistance |35. With the connections shown, positive pulses will be' formed in the circuits of condensers |24, |26 and |3| at the start of mark and negative pulses at the end of mark, but amplier tube |23 will reverse the pulses produced in the circuit of condenser |24 so that positive pulses will be formed at the end of the mark. The pulses from condensers |28 and |3| are S. M. pulses and the pulses produced by condenser |24 and inverted by the tube |23 are E. M. pulses.

Fig. 4 illustrates the diagrammatic circuits of the signal regenerator indicated by block I4 of Fig. 1. The corrected local 42% cycle voltage is applied to transformer The terminals of the secondary of this transformer are connected to the condenser |52 and adjustable resistance |53 in series. The middle of the transformer secondary is grounded. 'I'he input terminals of ampliiler |54 are connected between ground and the upper end of resistance |53. tion, manual adjustment of the resistance |53 will vary the phase of the input voltage to this With this constructube. The output terminals are connected to the input terminals of pentode amplifier-limiter |55, similar to pentode 55 of Fig. 3. The plate terminal of the ampliiler-limiter |55 is connected to the positive terminal of the plate supply through resistance |56. The cathodes of all the tubes are grounded, as indicated, and other connections are standard. The output of this amplifier-limiter is a square wave of the corrected 42% cycle frequency.

Point |51 in the plate circuit of amplifier |55 is connected to one plate of the condenser |56 and the other plate is connected to the minus C terminal throughresistance |60. The condenser end of resistance |60 is connected to the control grid of pentode clipper I5 l l Point |51 is also connected to one plate of a c'ondenser |62 and the other plate is connected through resistance |53 to the control grid of the pentode clipper |54. 'Ihe control grid of this tube is also connected to an intermediate point in the resistance |65, which has one end adjustably connected tothe negative bias source |56 and the plate of amplier |61. The cathode of the amplifier |61 is connected to the grounded minus B terminal and the grid is connected to signal load resistor |66 and to the plus B terminal through suitable resistances, so that the signal marks applied asa negative input as invFig. 3 make the grid negative with respect to the cathode. This rectified signal energy may be considered as coming from the amplirier-rectier I3 of Fig. 1.

The pentodes |5| and |64 are connected to the positive plate supply through resistances |10 and I1 I, respectively. 'I'he plate terminal of pentode I 64 is also connected through resistances |12 and |13 to ground.

A Finch locking circuit, generally indicated at |14, consists of dual amplier tubes |15, |15. The cathodes of the pairs of tubes are grounded and the plates of the pair |15 are connected to the grids of pair |15 through a suitable resistance |11. The plates of pair |15 are connected to the grids of pair |15 through resistance |15. The plates of pair |15 are connected to the plates of pair |15 through load resistance |19. The positive B terminal is adjustably connected to the middle of load resistance |19 and output terminals 60, |8| are adjustably connected thereto. i'hcse terminals are connected to relay coil I5 of The control grids of the pair of tubes |15 are connected through condenser |62 to the anode of diode |63 and the cathode of this, diode is connected to the plate of clipper |6I and a resistance |64 is shunted around the diode. The grids of the pair of tubes |15 are connected through condenser |55 to the anode of diode |66 and the cathode of this diode is connected to the plate of clipper |64. The anode of this diode is connected to the junction point of resistances |12 and |13. With this arrangement, the cathode of the diode is normally biased positive with lrespect to the anode, for a purpose to be later explained. The grids or pairs of tubes |15 and |16 are connected together through resistances |61, |66 and the terminal or the negative bias source is con-A denser 88a. 'I'his raises the plate potential of wave form-of the voltage applied respectively to the input terminals of triodes B2 and 82a, which is ampliiled and clipped by pentodes 88 and 88a. The rectangular plate voltage of pentodes 68 and 88a will be as given in graphs C and G, respectively. v l

In the CR differentiating circuit 12, 13, 14, positive and negative pulses will be formed. These will be superimposed on the signal (graph A) in the output of keying triode 8|. Therefore, the voltage applied to the input circuit of pentode-limiter will appear as indicated in graph D. This pentode has the cut-oliA indicated at |89 and only the positive pulses |9 |92, |93 in the marks will cause the pentode to conduct. These pulses will appear as dips in the plate voltage of the pentode, but they will be,

reversed and appear as positive pulses in the plate voltage of tube 18, as shown at |91, |98 and |99 in the 'graph E. In the lower chain of circuits of Fig. 3, the CR differentiating circuit 12a, 13a, and 14a will produce positive and negative pulses. These likewise will be superimposed on the incoming signal of graph A in the input circuit of pentode 15a and will appear, as indicated in graph H. Pentode 15a has the negative bias cut-olf indicated at 200 and therefore only the positive pulses I, 202 and 203 will cause the pentode to conduct. These voltage charges appear as pulses 204, 205 and 209 in the output of tube 18a (graph I) Whne the E. F. E. pulses |91, las and les" and the S. B. E. pulses 204, 205 and 206 are being formed from the local frequency, as just described, the incoming rectangular signal across resistance 19 is producing S. M. pulses 201 and 208 at the beginning of each mark and negative E. M. pulses 201 and `208' in the circuits containing condensers |24, |28 and |3| at the end of the marks, as indicated in graph J. The pulses produced in the circuit containing condenser |24, however, will be reversed 180 in phase by the amplifier tube |23 and the negative pulses shown become positive pulses '209 and 2|0. As will later be apparent, only the positive pulses will be effective as controls.

'Let it now be assumed that the` local frequency oi' 42% cycles has the desired phase relation with the incoming signal. When the start of, mark pulse 201 of graph J is formed in the circuit of condenser |28, it fires thyratron 92a. Condenser 89a instantaneously discharges through this thyratron down to about 15 volts, whereupon the thyratron extinguishes. 'Ihis insures that the condenser 89a always starts charging from the same reference level of about 15 volts. tron 92a extinguishes when this voltage is reached, because the charged condenser; supplies the only potential that is in its plate circuit.' When thyratron 92a res, thyratron |03 is extinguished by action of the commutating condenser |06. The reason for this is well known, but an explanation of it may be found in the patent to G. R. Clark, No. 2,237,522, April 8, 1941.

The extinguishing of thyratron |03 decreases the negative bias on thyratron 84, due to the elimination of the drop in resistance |01 in the voltage divider circuit. Thyratron 84 is thus in condition to be fired by the E. F. E. pulse, as will later be explained.

At the time condenser |28 forms S. M. pulse 281, the circuit of condenser |3| forms an identical pulse of like phase, which ignites thyratron 84a. I'he firing of thyratron 84a extinguishes thyratron 85a, by the commutating action of con- Thyrav 85a by removing the plate current drop in vresistance 81a and condenser 89a starts to charge. 'Ihis continues up to point a of graph K, when the E. F. E. pulse |9| is formed and ignites thyratron tube 85a. This extinguishes thyratron tube 84a by commutation. The plate voltage of 85a is lowered by the drop in resistance 81a and condenser 89a stops charging at point a. This condenser cannot discharge through thyratron 85a at this time, as the diode 90a will not conduct in the reverse direction. It therefore holds its charge for comparison with the charge in condenser 89 at the start of the next space. The firing of thyratron 85a lowers the bias potential on the grid of thyratron |03, which prevents the subsequent S. B. E. pulse from igniting it, but this has no effect on the controls except when the pulses from the local source have been reversed with respect tol the signal, as will later be explained.

At the time thyratron 85a is fired by the E. F. E. pulse |91, thyratron 92 is ired by an identical pulse passing through coupling condenser ||0 and this discharges condenser 89 down to reference level of about 15 volts. This occurs at the point b of graph L. At exactly this time, E. F. E. pulse |91 fires thyratron 84 through coupling condenser' I3, which simultaneously extinguishes thyratron 85. Therefore, condenser`89 starts to recharge and will continue charging until lthe S. B. E. pulse 204 forms, at which time condenser 89 is discharged to reference -level again at point c. Since thyratron 85 is still non-conducting, condenser 89 will charge from reference level to the point d of graph L, at which time the E. M. or end of mark pulse 209 in graph J will appear in the circuit of condenser |34, which fires thyratron 85. This stops thecharging of condenser 89 at the point d of graph L. Since we have assumcd that the local frequency is in correct phase relation with the incoming signal, the time of charging of condenser 89a will be equal to the time of charging -of condenser 89, because the E. F. E. pulse |91 and the S. B.\ E. pulse 204 are equally spaced from the beginning and the endV of the mark, respectively. Therefore, when this end of the mark occurs at point f of graph A, the relay tubes 93, 94 will be unblocked by elimination of the negative potential across the signal load resistance 19 in their grid circuits. Since condensers 89 and 89a have equal charges, the grids of tubes 93,' 94 will have equal potentials and the cathode current of these two tubes will ance 19 during mark, as the circuit resistancev isv too great for this.

Condensers 89 and 89a will hold their charge until the start of mark at point g of graph A. The S. M. pulse produced in the circuit of condenser |28 lires thyratron 92a and discharges condenser 89a down to reference level at point h of graph K. Simultaneously, the S. M. pulse in the circuit of condenser |3| fires thyratron 84a.

and thyratron a is simultaneously quenched by 'commutating action. Thus, condenser 89a.im

m has its grid ptenuai raised at this time so that the S. B. E. pulse can later ilre it. When at i of graph L, but immediately starts recharging because thyratron 85 is now quenched. Condenser 89 therefore charges up to the point lc when the S. B. E. pulse 285 is produced and discharges the condenser again by igniting thyratron 92'through condenser ||5. Condenser 89V again recharges, because thyratron 85 is still quenched. When the E. F. E. pulse |99 occurs at the point l, condenser 89 is discharged again to reference level and charges up to the point m, when the S. B. E. pulse 288 ignites thyratron 92 and again discharges the condenser to reference level. kIt then charges up to point n and E. M. pulse 2|8 iires thyratron 85 and stops the charge at this point.

After the point i was reached in graph K, the subsequent occurrence of the E F. E. pulse |99 and S. B. E. pulses 285 and 288 in the multiple mark had no effect on the condenser 89a. Therefore, the condensers 89 and 99a at the end of the multiple mark have been charged during an equal length of time and when the tubes 93 and 94 are unblocked at the end of the multiple mark there will again be no movement of the tongue of relay 36.

This stops theof thyratron 85a reduced the negative potential on its grid so that this could take place. The firing of thyratron |88, however, has no etl'ect at this point. S. B. E. pulse 2| I also fired thyratron 92, which discharged condenser 89 to reference level at the point q in graphO. When the misplaced E. F. E. pulse 2 |2 is reached, the charging of condenser 89a is stopped by the ring of thyratron 85a. This occurs at the point p of graph N and condenser 89a holds its charge at this level. When the misplaced E. F. E. pulse 2|2 occurred, thyratron |89 was conducting and fore, at the end of the single mark, condenser 89a has a greater charge than condenser 89, as will be apparent by comparing graphs N and O at this point. Thus, relay 38 will operate and start the correcting action.

When the start of the multiple mark occurs at g of graph A, the condenser 89a will be dis. charged, as in the case of the single mark, and

I it will charge up as before until the misplaced Now let it be assumed that the phase of the local source of frequency is leading the incoming signal. 'I'his means that the pulses |91, |98 and |99 oi' graph E will be nearer the front end of the signal mark, while the S; B. E. pulses 284, 285 and 286 will be farther away from the end of the signal mark. Therefore, condenser 99a will charge up to a less voltage than condenser 89 and when the bias is removed from tubes 93, 94 at the end of the mark, there will be a. greater current passing through the upper coil of relay 36 than is passing throh the lower coil. The tongue of the relay will now be swung against the contact, say the positive contact, to rotate the plate 58 ot Fig. 2 in a direction to bring the local frequency back into phase with the incoming signal. This action is repeated at the end of each single or multiple mark until the phase displacement is corrected. condensers 91 and 98 have an integrating elect in respect to the current pulses in the circuit of tubes 93 and 94, so that actual movement of the relay tongue takes place usually after a plurality of small charges are added to the condensers 89, 89a.

Let it also be supposed that in starting up the system, or for some other reason, the phase of the local frequency is reversed from that shown in graphs B and F of Fig. 5. When this occurs, the E. F. E. and S. B. E. pulses will be transposed, as indicated in graph M. At the start of the mark at point o in graph N, the thyratrons 92a and 84a are red and thyratrons |83 and 95a are extinguished, in the way previously described. Condenser 89a then discharges to reference level at o and immediately starts charging. When the misplaced S. B. E. pulse 2|| is reached, it has no eiect on the charging of condenser 89a because the lower chain of pulse circuits, as before, has no eiect on this condenser.- The S. B. E. pulse 2|| igntes thyratron |83 because the quenching E. F. E. pulse 2|9 is reached,I whereupon the charging of condenser 89a will cease. When the previous S. B. E. pulse 2|4 occurred, it would have caused condenser89 to discharge down to reference level if it had not already been discharged at the point q in the single mark. 'I'herefore, condenser 89 is at reference level. When the S. B. E. pulse 2| 4 was reached, it energized thyratron 92, but this had no effect on condenser 89, as it had already been discharged to reference level. The S. B. E. pulse 2|4 ignited thyratron |83, as previously explained in connection with the single mark, and this reduced the negative bias on thyratron 84 and prevented its being flred by E. F. E. `pulse 2|8. It will be evident that the misplaced subsequent S. B. E. and E. F.

-E. pulses 2|5 and 2|8, respectively, will not cause condenser 89 to charge. Therefore, at the end of a multiple mark, 'the charges on condensers 99 and 89a are the same as at the end of a single mark; that is, they have unequal charges and relay 38 will be operated and cause correction to take place. Thus, the occasional failure occurring in the prior system referred to has been obvlated in our invention.

The operation of the signal regenerator of Fig. 4 will now'be described:

The voltage of the corrected local source of 42% cycles per second is applied to transformer |5|. This local source has a sine wave form, as previously stated, but the pentode limiter |55 converts this into a rectangular wave, as indicated by graph P of Fig. 5. This rectangular voltage wave of 42% cycles charges both the condenser 58 and the condenser |62. A typical current pulse in condenser |58 is indicated by the graph 0. p, 1' of Fig. 6. Graph Q of Fig. 5 indi.- cates the actual potential applied from the drop in resistance |68 to the control grid of the pentode |6|, the cut-off being indicated at |89. Graph o, p, s similarly illustrates the current pulse of condenser |62.

Resistor |53 of the phase,` shifter is so adjusted that the positive pulses of graph Q occur, say, in

the exact 'center of the signal bauds introduced the charging and discharging pulses of conden` ser |82 will be combined with the signal wave, as indicated in graph R. The pentode |64 is biased almost to cut-olf, as indicated at 2|1. The pulses of condenser |58 occur simultaneously with the pulses of condenser |62, but' they are not superimposed on the signal. The cut-ofl.' of pentode .|84 eliminates the effect of the negative puls'es in the plate circuit of the pentode as well as the positive pulses in the centers of the space bauds. Pentode |64 will therefore conduct current slightly during the marking bauds and will amplify pulses 2|8, 2|8 and 228.

The pulses from condenser |58 alone will con trol the conducting condition of pentode ISI. The cut-olf point 2|8', as indicated in graph Q, is such as to eliminate all negative and background pulses in the plate circuit and the tube will conduct current only at points 22| to 225, inclusive.

The pulses produced by the charging of condensers |58 and |62 will simultaneously unblock pentodes |6| and |64 at the centers of the mark bauds, but, as will be apparent from an inspec.. tion of the discharge curves of Fig. 6, pentode |64 will bev conducting for the greater time and therefore will control-the locking circuit.

When the mark baud 226 of graph R occurs, the voltage at point 226 starts tube |64 conducting slightly, but the current does not produce suiiicient drop in resistance/I 1| to reduce the potential of the cathode of the diode |86 to that of its anode, so locking circuit condenser |85 cannot discharge through this diode. When the pulse 2|8 of graph R is reached, this current isy suicient to render this diode conducting. Con-1 denser |85 then discharges through the diode and pentode |64. The discharge current passes to ground, to the negative lbias terminal and through resistance |88 to the negative plate of the condenser. This increases the bias on the grids of the pair of tubes |16 of the locking circuit and quickly reverses it due to 'the' cross grid plate connection. At this time condenser |58 discharges also, but the discharge of condenser |62 prevails, as it unblocks pentode |64 for a longer time. Thus, locking tubes are made conducting and tubes |16 are blocked. This makes the conductor |8| positive and conductor |88 negative. A regenerated mark baud is thus started at 221 of graph S.

The locking circuit continues without change until pulse 222 of graph Q is produced and makes pentode |8| conducting. This discharges condenser |82 through the low resistance path of diode |83 and pentode |6I. There is no pulse in the input circuit of pentode |64 at this point, as l shown by graph R, and therefore condenser |85 cannot discharge. The 'discharge of condenser |82 throws the locking circuit and reverses the polarity in load resistance |19. This starts the space at point 228 of graph S. It will be apparent without further description that pulse 2|8 will ing currents will not unbalance the locking circuit.

Condenser |85 will be discharged by pulse 228, but since the locking circuit is already conducting in the direction that this would throw the circuit, this discharge has no eiiiect.l

. It might be thought'that the cut-oil point 2|1 could be placed at the exact top of the signal in graph R and thus make it unnecessary to use the negative bias on diode |88. However, it is diilicult to do this as a practical matter and it has been found highly advantageous to use this bias in the way disclosed.

We have disclosed a particular embodiment for carrying out the principles of our invention, but this has been by way of example only. Various other embodiments may be devised without departing from the spirit of the invention,4

Having described our invention, what we claim is:

1. In a. system for regenerating telegraph signals, means-for producing a ivrst and a second train of pulses simultaneously at predetermined points of the mark and space bauds having frequencies equal to the signal baud rate, the voltages of all of the pulses at their start being substantially the same but thereafter the voltages of the pulses of the rst train being greater than those of the second train, a pair of tubes and means to cause one tube to conduct by the action of the pulses of the -rst train during signal marks and the other tube to conduct by the action of the pulses of the second train during signal spaces.

2. In a system for regenerating telegraph signals, means for producing a rst and a second train of pulses simultaneously at substantially the centers of the mark and space bauds having frequencies equal to the signal baud rate, the voltages of all of the pulses at their start Vbeing substantially the same but thereafter the voltages of the pulses of the rst train being greater than those of the second train, means for combining the pulses of the first train with the signals, a pair of tubes and meansto cause one tube to conduct by the combined signals and pulses of the rst train during signal marks and the other tube to conduct by the pulses of the second train during signal spaces.

3. In a system for regenerating telegraph sig'- to cause one tube to conduct by the action of the combined signals and pulses of the first train during signal marks and the other tube to conduct' by the action of the pulses of the second train during signal spaces.

4. In a system forregenerating telegraph signals, means for producing a first and a second train of pulses having frequencies equal to the signal baudrate, the pulses of the first train predominating those of the second train, means the signals and applying them to the input circuit ofthe first amplifier tube, means for applying the pulses of the second train to the input circuit of the second amplifier tube, means for biasing the input circuit of the first amplifier tube to conduct only during the signal mark bauds, a pair of resistances, the output terminals of each amplifier tube being connected to the power supply through one of said resistances, a

condenser and a diode connected in series between a point in each of said resistances and the cathode of each amplifier, and a resistor connected in parallel with each diode, said diode being so poled that the condensers can discharge but not charge through said resistor.

5. In a system for regenerating telegraph signals, means for producing a first and a second train. of pulses having frequencies equalto the signal baud rate, the voltages of all of the pulses at their start being substantially the same but thereafter the voltages of the pulses of the rst train being greater than those of the second train, means for phasing the pulses of both trainsl at predetermined points of the signal mark and space bauds, a first and a second amplifier tube, means for combining the pulses of the first train with the signals and applying them to the input circuit of the first amplifier tube, means for l applying the pulses of the second train to the input circuit of the second amplifier tube, means for biasing the input circuit of the first amplifier tube to conduct only during the signal vmark bauds, a pair of resistances, the output terminals of each amplifier tube being connected to the power supply through one of said resistances, a condenser and a diode connected in series between a point in each of said resistances and the'cathode of veach amplifier, and a resistor connected in parallel with each diode, said diode 'being so poled that the condensers can discharge but not charge through said resistor.

Cal

6. In a system for regenerating telegraph signals, means for producing a first and a second train of pulses at substantially the centers of the signal mark and space bauds having frequencies equal to the signal baud rate; the voltages of al1 lof the pulses .at their start being substantially the same but thereafter the voltages of the pulses of the first train being greater than those of the second train, a first and a second amplifier tube, means for combining the pulses of the first train with the signals and applying them to the input circuit of the first amplifier tube, means for applying the pulses of the second tube, means for biasing the input circuit of the first amplifier tube to conduct only during the mark bauds, a pair of resistances, the output terminals of each amplifier tube being connected to the power supply through one of said resistances, a condenser and a diode connected in series between a point infeach of said resistances and the cathode of each amplifier, and a resistor connected in parallel with each diode, said diode being so poled that the condensers can discharge but not charge through said resistor.

7. In a system for regenerating telegraph signals, means for converting the signals into rectangular form, means for producing a first and a second train of pulses at substantially the centers of the signal mark and space bauds having frequencies equal to the signal baud rate, the voltages of all of the pulses at their start` being substantially the same but thereafter the voltages of the pulses of the first train being ygreater than those of the second train, a first and a second amplifier tube, means for combining the pulses of the first train with the rectangular signals and applying them to the input circuit of the first amplifier tube, means for applying the pulses of the second train to the input circuit of the second amplifier tube, means for biasing the input circuit of the first amplifier tube to lconduct only during the signal mark bauds, a

pair of resistances, the output terminalsof each amplifier tube being connected to the power supply through one of said resistances, a condenser and a diode connected in series between a point in each of said resistances and the cathode of each amplifier, and a resistor connected in parallel with each diode, said diode being so poled that the condensers can discharge but not charge through said resistor.

8. In a system for regenerating telegraph signals, means for producing a first and a second train of pulses having frequencies equal to the signal baud rate, the voltages of all of the pulses at their start being substantiallyv theI same but thereafter the voltages of the pulses of the rst train being greater than those of the second train, means for phasing the pulses of both trains at substantially the centers of the mark and space bauds, a first and a second amplifier tube, means for combining the pulses of the first train with the signals and applying them to the input circuit of the first amplifier tube, means for applyying the pulses of the second train to the input circuit of the second amplifier tube, means for blocking the first amplifier tube slightly below the peak of the signal mark voltage, a pair of resistances, the output terminals of each amplifier tube being connected to the power supply through one of said resistances, a condenser and a diode connected in series between a point in each of said resistances and the cathode of each amplifier, a resistor connected in parallel with leach diode, said diode being so poled that the condensers can discharge but not charge through i said resistor and means to produce sufficient vduring the occurrence of the pulses of the first train in the mark bauds.

9. In a'. regenerating system for telegraph signals of a predetermined baud rate, a local source of alternating voltage having a. frequency proportional to .said baud rate, means for producing a wave train of voltage pulses having a frequency proportional to the frequency of said alternating voltage, means for phasing the pulses of said wave train with the center of the signal bauds, means for combining the pulses with said signals, an amplifier biased to cut off slightly below the base of the positive ones of the pulses in the mark bauds, a diode and a condenser connected in series across theoutput circuit of the amplifier with such polarity of the diode as to prevent charging of the condenser therethrough,l

a resistance around the diode to provide for charging of the condenser and means to render the cathode of the diode negative with respect to the anode thereof when the combined voltage of the mark bauds anrll pulses is applied to the input circuit of the amplifier,

10. In a system for regenerating telegraph signals, means for converting the signal marks into rectangular form with a pulse at the center of each baud thereof, a locking circuit, a diode, a

potentiometer, a condenser in the input circuit of said locking circuit, said condenser and diode being connected in series across a portion of said potentiometer and poled so that .the kcondenser can discharge but not charge through the diode, an amplifier tube having its output circuit connected across a portion of said potentiometer l and means for applying the rectangular signal marks and the associated pulses to be input terminals of said amplifier, the potentials-of the input and output circuits of said amplifierbeing such that the condenser can discharge through the diode when amplifier input. y 11. In systems for phasingand regenerating telegraph signals of a predetermined lbaud rate,- a local source of alternating voltage having a, fre.v

quency proportional t0 said baud rate, meansfor producing from said source first and second trains of voltage pulses ofsaid frequency separated from each other by a predetermined phase angle, means forproducing from said local source third and fourth vequi-phased wave trains..

of voltage pulses of said frequency, respectively lagging and leading the first and second wave trains by equal angles, a first. and a'lsecond condenser, means'for chargingsaid first and second lsaidpulses are lapplied to the.'

proportional to rsaid baud rate,- means for nor' Amally producing a backeend pulse in the second l.. v14. In phasing systems for4 reception graph signals of predetermined baud rate, a vlocal 13. In phasing systems for reception of telegraph signals of predetermined baud rateja local source of alternating voltage having a frequencyr proportional to saidvb'aud rate, meansffor normally producing a back-end pulse inthe`v second half of a mark baud of said frequency, aba-ckend condenser, means for charging "said, con- )denserA during 'the time elapsing between the back-end 'pulse occurring in the last half of the last baud of a signal mark and the end thereof andmeans for preventing the charging of said 'back-end condenser upon the'f abnormal occurrence of said back-end pulse in the baud of a` signal mark.

first half of a source of alternating voltage having `a frequency half of agmark, baud of saidfr'equency, ra backend `rcondenser, means.; for chargingl said 'condenser. during the time "',elapsing between the back-end pulse in the last baud of a signal mark and the end .thereof and means for discharging said back-end condenser upon the abnormal occurrence of `saidback-end pulse in the first half v of a baud of a signal mark. f

condensers proportionalv to the phase angles bev tween predetermined pulses of' the first and sec,-

ond trains and the start and end of the marks,

respectively, means controlled by the difference in the charges of said condensers for. shifting Vthe phase of the local alternating voltage to cause the first and secondwave trains to lead `and lag the signal baud centers by equal phase angles l5. In phasing systems for reception of telegraph signals of predetermined baud rate, a local source of'alternating voltage having a lfrequency proportionall to said baud rate, means for normally producing a back-end pulse in the second and the third and fourth wave trains to be iny phase therewith, means fork producing a 'regenerating voltage of one polarity at the occurrence v of a pulse of the third wave train in a predeter-l mined baud of a. mark and for producing `a regenerating voltage of opposite polarity atfthe occurence of a pulse ofthe fourth wave train in a corresponding baud of the followingr space. l

12. In systems for phasing andf'fegenerating 'Y telegraph signals of -a Api'edetermine-d b a local source of alternatingfvolt' frequency proportional to` saidffbaudlratetmeansfor producing fromv said vsource first and second trains of voltage pulses ofj` said frequency sepa.` rated from each othergbyl a predetermined phase angle, means for producing'from said local sourceV third and fourth equi-phased wave trains of voltage pulses ofV said frequency, respectively lagging and leading the first and'second wave trains by equal angles, a-rst and a second condenser, means for charging Athe first condenser propor- .graph signals Yo, p source of alternating voltage having a frequency half` of a mark baud of said frequency, a backend condensenmeans for charging said condenser during vthe time elapsng between the vbackfend pulsein the last baud of a mark and the end thereof and means for discharging said back-end condenser,- and preventing its recharg- .ing upon'. they abnormal occurrence yof saidbackend pulse in the first half of a mark baud.

16. In phasin systems 4for reception o f teleredetermined baud rate, a local proportional-rtofs'aid baud rate, means vfor normallyproducing'fi the firstA and second halves',

of a', mark ybanniv frontand back-end pulses, ref` z'spectively.` of said frequency separated by a predetermined pha'se angle, frontand back-end condensers, means for charging the front-end condenser during the time elapsing between the `s`tar`t`=o-f the mark and the first front-end pulse,

meansk for charging'ithe back-end condenser duringthe ktime elapsing between the back-end pulse a l inthe last baud of `a mark and the end thereof,

ris

tional to the phase angle between the startfof a.rv`

mark andra pulse of the first Wave train occurring in the first baud thereof and for charging said second condenser proportional to the phase angle between the end of the mark and a pulse of the secondwave train occurring in the' last baud thereof, means controlled bythe differencer in the charges of said condensersforgshifting. the I phase of the local alternating'rvoltagefto ,cause the first and second wave trains `to lead'gand'lag the signal baud centers by equaljphase angles and the third and fourth wave trains'to be in phase therewith, means for producing a regenerating voltage of one polarity at thefoccurrence of` a pulse of the third wave train in thefirst baudy of a mark and for producing a regenerating voltage of opposite polarityat the occurrence of a" pulse of the fourth wave train in the lfirst baud of the following space. i.

'meansforpreventingthe charging of the backfendicondenser when inv abnormal operation the back-end pulse y.precedes jthe Ifront-end pulse in a 'mark and means'controlled? by a difference in the charges. ofsaidconde'nsers during the space vbauds, for' adjusting the phase of said local'- source until the said angle is bisected by the centers of the bauds ofthe'` mark with the frontand backend `ypulse's occurring in the first and second halves, respectively, thereof. f

l1"?, In phasingy systems for reception of'telegraph signals ofppredetermined baud rate, a local `source of alternating voltage havingY a frequency proportional to said baud rate, means for norof tele- I ing the time elapsing between the back-end pulse in the last baud of a mark and the end thereof and means for preventing the charging of the l back-end condenser when in 'abnormal operation the back-end pulse precedes the front-end pulse in a baud of a mark.

18. In phasing Ysystems for reception of telegraph signals of predetermined baud rate, a local source of alternating voltage having a frequency proportional to said baud rate, means for producing frontand back-end pulses, respectively, of said frequency separated by a predetermined angle and normally positioned in the rst and second halves, respectively, of a mark baud, frontand back-end condensers, means for starting the charging of the front-.end condenser at the start of the mark and stopping the charge uponX the occurrence of the first front-end pulse, means for starting the charging of the back-end condenser upon occurrence of a back-end pulse in the last baud of a mark and stopping the charge at the end of the mark, means for =preventing `said charging of the back-end condenser upon reversal of the positions of the frontand backend pulses in abnormal operation and means controlled by a diilerence in the charge of said condensers `during the space bauds for adjusting the phase of said local source until the said angle is bisected by the centers of the bauds of the mark with the pulses occurring in their normal position.

19. In telegraph phasing systems having signals of predetermined baud rate, a local source of alternating voltage having a frequency proportional to said baud rate, means for producing frontand back-end pulses of said frequency separated by a predetermined angle and normally positioned in the rst and second halves, respectively, of a mark baud, frontand back-end condensers, means for discharging the front-end condenser at the start of the mark and thereupon recharging it until the occurrence of the first front-end pulse in the mark, means for discharging said back-end condenser and thereupon recharging it upon the occurrence of a front-end pulse and a back-end pulse in a mark baud in their normal position, means for stopping the charging of the back-end condenser at the ends of the marks, means for discharging the backend condenser and preventing its recharging lupon interchange oi' the frontand back-end pulses in abnormal operation and means controlled by a diierence in the charges of said condensers during the space bauds for adjusting the phase of said local source until the said angle is bisected by the centers of the bauds of the marks with said pulses occurring in their normal posi- 20. In a system for regenerating telegraph signals, means for producing a ilrst and a second train of pulses simultaneously at predetermined points of the bauds having frequencies equal to the signal baud rate, the pulses of both vtrains having substantially-the same voltage at, their start but those of the tlrst train having greater voltage thereafter, means for combining. the signal marks and spaces with the pulses of the iirst train, a rst and a second tube, means for blocking either tube when the other one conducts, means for feeding the combined signals and pulses of the rst train .to the input circuit of :the first tube and the pulses of the second train to the input circuit of the second tube, and

a utilization device connected in the output circuit of said tubes. i

21. In a system for regenerating telegraph sig nals, means for producing a first and a second train of pulses simultaneously at predetermined points of the bauds having frequencies equal to the signal baud rate, the pulses of both trains having substantially the same voltage at their start but those of the rst train having greater voltage thereafter, means for combining the signal marks and spaces with the pulses of the rst train, means for threshold limiting the combined signals and pulses of the nrst train slightly below the maximum value of the signal marks, av

first and a second tube. means for blocking either tube when the other one conducts, means for WARREN A.. iNDERs'oN. 

